The present invention relates to an image display system for displaying interlaced images (of television and laser disc signals) on non-interlace display apparatuses, such as those used in personal computers (PC).
According to the prior art, video signals from television or laser discs are sometimes inputted to a PC and displayed on its screen, and these input signals constitute what are called interlaced images in which even-number fields and odd-number fields are alternated every 1/60 second. These signals comprising even-number and odd-number fields are together referred to as frames. An example of such display apparatus according to the prior art is disclosed in the U.S. Pat. No. 5,068,648.
When interlacing signals are to be used for displaying non-interlaced images on a PC screen, conversion from inter lace to non-interlace is required.
According to the prior art, interlacing signals from the input source are once stored in a memory known as a frame buffer, end when they are read out of the frame buffer, they are converted into non-interlacing signals to display non-interlaced images on the PC screen.
FIG. 6 illustrates conventional methods of interlace-to-non-interlace conversion: (a) shows a single buffer system, (b), a double buffer plus frame display system, and (c), another double buffer plus frame display system.
In the single buffer system shown in FIG. 6(a), the same buffer is used as read buffer for display indication and as write buffer for the input source.
In the double buffer plus frame display system shown in FIG. 6(b) (hereinafter called Double Buffer System 1), the read buffer for display indication and the write buffer for the input source arm separate, and the fields are displayed at a rate of 30 frames per second (fps).
In the double buffer plus frame display system shown in FIG. 6(b) (hereinafter called Double Buffer System 2), the read buffer for display indication and the write buffer for the input source are separate, and each even- or odd-number field is displayed at a rate of 60 fps. In display indication, each field is extended vertically, and interpolation lines are inserted into the spaces between fields.
The methods described above involve the following problems.
(1) Single Buffer System
An both fields of input interlaced images are displayed as single images, resolution in the vertical direction is high, resulting in clear displaying of still or slow-moving images, but fast-moving images are subject to motion artifacts on the contours of moving objects corresponding to time differences between fields (1/60 second), resulting in blurred contours.
As the speed of writing from the input source is constant in this systems while computers or the like use faster display apparatuses, reading from the frame buffer may over-take writing from the image input source to the frame buffer and, if it does, an image under updating is displayed.
(2) Double Buffer System 1
Since an update buffer and a display buffer are separately provided, there is no possibility for an image under updating to be displayed. However, as the even-number and odd-number fields of each input interlaced image are displayed as a single frame, fast-moving images are subject to motion artifacts on the contours of moving objects corresponding to time differences between fields, resulting in blurred contours.
(3) Double Buffer System 2
Since each even-number or odd-number field of the input interlaced image is displayed as a single frame, even fast-moving images are immune from motion artifacts due to differences in motion corresponding to time differences between fields, but the height of the frame is doubled when displayed and interpolating lines are inserted between the original lines, resulting in poor resolution in the vertical direction and consequent deterioration in picture quality.
Moreover, as most such methods do not take into consideration the correlation between one field and the next in inserting an interpolating line as mentioned above, the displayed image, especially where a striped pattern is involved, may turn out completely different from the original image.
The present invention, worked out in view of the above-described problems involved in the prior art, is intended to provide an image display system subject to no conspicuous motion artifact ensuing from differences in motion corresponding to time differences between fields.